1. Field of the Invention
The invention relates to chill-free foundry irons usable in foundry production.
2. Description of the Prior Art
USSR Inventor's Certificate No. 380,736 discloses a foundry iron consisting essentially of, in per cent by weight:
______________________________________ carbon from 3.5 to 4.3 silicon from 1.0 to 2.9 manganese from 0.05 to 0.8 aluminium from 0.03 to 0.2 calcium from 0.005 to 0.08 magnesium from 0.01 to 0.1 sulfur up to 0.01 phosphorus up to 0.01 iron the balance ______________________________________
However, castings of this foundry iron have a chilled surface layer of low mechanical properties and are difficult to machine.
Due to the chilled surface, castings of said foundry iron have to be annealed in heat treatment furnaces with the aim of improving the mechanical properties of the surface layer of the castings and the machinability thereof.
Annealing of iron castings improves the mechanical properties of the surface layer and the machinability of the castings, but impairs other properties of the basic metal and substantially raises the cost of the castings.
Attempts have been made to provide a foundry iron that would be free of chill on the surface. Such a foundry iron is disclosed in USSR Inventor's Certificate No. 377,394, the chemical composition of the foundry iron being, in per cent by weight:
______________________________________ carbon from 2.8 to 4.0 silicon from 0.3 to 0.9 manganese from 0.2 to 1.2 lanthanum from 0.0002 to 0.1 cerium from 0.0005 to 0.1 neodymium from 0.0001 to 0.1 praseodymium from 0.00005 to 0.1 one of the ele- ments: samarium, gadoli- nium, terbium, europium, dys- prosium, holmium, erbium, thulium, ytterbium, lute- cium from 0.00015 to 0.1 sulfur up to 0.15 phosphorus up to 0.30 iron the balance ______________________________________
This foundry iron is suitable for the production of castings free of surface chill, 4 mm thick and over, said iron, however, being costly as it contains rare-earth metals.
In addition, said foundry iron cannot be used to manufacture castings of complicated configurations and sections less than 4 mm thick, or castings poured in metal, or other types of rapid-cooling moulds.
Due to an increase in the output of parts cast into metal moulds and to a need for minimizing the consumption of metal in foundry production, there is an urgent need for devising a means to produce castings of chill-free surface. The unavailability of such a foundry iron results in considerable difficulties in machining of castings and raises the cost of their manufacture.